ASTEROID - A research project concerning the aerodynamic effects of small changes of
aircraft shape; developing methods for use by the aircraft design industry for the
optimisation of aerodynamic cleanliness in manufacture, maintenance and repair.

Completed August 2018

The Objective of the Research

The objective of this research project was to develop improved
computational methods to determine the aerodynamic effects of
small local changes in external shape and airflow – (i.e.
excrescences, surface deviations and airflow leakage).

The project developed methods to quantify the effects on
aeroplane performance of: steps and gaps between adjacent
panels, small protuberances, holes and indentations, external
repair patches; and also of airflow leakage arising from ineffective
sealing between components.

Context of the Research

All structures, including airframes, are manufactured and assembled to specified tolerances.
In general, the smaller (tighter) the tolerances, the higher will be the cost of manufacture. It is
not possible to build an aircraft (including all joints, fairings, cowlings and doors) to exactly
the shape set out in the design - i.e. the optimised shape for highest performance and
minimum fuel burn. This project has delivered improved tools that design and manufacturing
organisations could use to quantify the performance penalties arising from deviations from
the design and so enable the trade-off between manufacturing tolerances and aircraft
performance to be quantified.

Once in-service the external ‘cleanliness’ of an aircraft will reduce due to the general ageing
of paint and seals and the deterioration in the alignment of cowlings, doors and other
moveable components. In addition, if an aircraft suffers damage in service, choices have to
be made about the nature of the repair – whether it will restore the original shape (usually the
most expensive option) or whether it is acceptable to change the external profile by adding an
external plate to cover the damaged area. This project has delivered a design tool that can be
used to quantify the drag reductions (and therefore fuel and emissions savings) that may be
achieved by optimising repairs and the fit of components in service.

The Research and Development Programme

This research and development programme includes the following work packages:

A comprehensive review of current methods and data for the effects of surface deviations,
excresences and leakage. This work package reviewed and documented the past research
and existing methods and data and so identified the areas where new data was acquired for
the development and validation of improved modelling.

Wind tunnel testing. The ASTEROID project performe wind tunnel tests to obtain new data
for method development and validation. Low speed tests were completed at Cranfield
University and at City University. Transonic testing was carried out at the University of
Cambridge.

Integral Boundary Layer (IBL) model development. Using flow measurements from the
wind tunnel tests and other data identified by the review, Computational Fluid Dynamics-
coupled IBL methods such as VGK (Viscous Garabedian and Korn) and VFP (Viscous Full
Potential) were modified to simulate the effects of typical excrescences.

Maintenance and repair. As part of the project IHS ESDU developed an enhanced user
interface for ESDU excrescence drag methods that enables designers to calculate rapidly
and repeatedly the drag effects of excrescences. This will enable designers to optimise the
specification of manufacture, repair and maintenance instructions.

RANS-based Surface Discontinuity modelling. A tailored Fluent User Defined Function
(UDF) that can locally manipulate the flow in order to simulate surface discontinuities using
Reynolds Averaged Navier Stokes methods was developed and validated as another method
for the determination of the aerodynamic effects.

The Primary Participants

IHS ESDU - ESDU (formerly the Engineering Sciences Data Unit) has a
long history
of developing aerospace design data and methods in the form of
"Data Items" and accompanying software. IHS ESDU methods are used by numerous design
organisations in the aerospace industry worldwide. The IHS ESDU methods are rigorously
validated by committees of technical experts. The
Transonic Aerodynamics Committee will
provide technical scrutiny of this project.

University of Leeds
- Specialists at the University of Leeds have long experience
in the field of aerodynamic design and research.

BHR Group
- Originally set up as the British Hydromechanics Research Association in
1947, BHR Group is now an independent engineering research and consultancy company based
on its core expertise in fluids engineering.

Funding

The ASTEROID project is 50% funded by the UK Government through
Innovate UK.

Project ASTEROID Timeline

The project was formally completed on 31st August 2018. The primary participants continue to
build on the achievements of the research for the further development of excrescence drag
methods.